Some Numerical Studies on Coupled Turbine–Generator Rotor System Models

Coupled turbine–generator rotor systems are unique in their vibration behavior compared to individual rotor systems. Changes in geometric and dynamic parameters of individual rotor systems and coupling affect the overall response. Since there is also bound to be inherent misalignment at the coupling location, along with residual unbalance in the system, the rotor response contains harmonics corresponding to both unbalance and misalignment. A coupled Jeffcott rotor system with central discs integrated with active magnetic bearing (AMB) is considered in this work. The mathematical model is formulated from four degrees of freedom coupled Jeffcott rotor systems using Lagrange’s equations. A SIMULINK^TM model is created to generate vibration and current responses in the time domain. Secondly, a full-spectrum FFT analysis of the time-domain signal is performed to examine the harmonics of the rotor’s vibration response and AMB’s current response. The change in the nature of rotors’ response for various permutations of unbalance and angular misalignment is studied. The advantage of full spectrum over time-domain signals and orbit plots in diagnosing misalignment has been demonstrated.